This invention relates to methods for producing (i) isomeric mixtures containing greater than 60% cis-2-methyl-3-pentenoic acid or lower alkyl esters thereof, and/or (ii) 2-methyl-4-pentenoic acid or lower alkyl esters thereof and/or (iii) 2-methyl-pentanoic acid or lower alkyl esters thereof, by means of hydrogenation of 2-methyl-3,4-pentadienoic acid esters and, if desired, hydrolysis thereof.
There has been considerable work performed relating to efforts to obtain inexpensive substances which can be used to impart (or enhance) flavors to (or in) various consumable materials. These substances are used to diminish the use of natural materials, some of which may be in short supply and to provide more uniform properties in the finished product. Sweet, fruity, strawberry, winey-cognac, butter-like, rum-like, butterscotch, cooked strawberry jam, pineapple-like, pear, green and applie-like aromas as well as sweet, strawberry, nutty-coconut, fatty, butter-like, rum-like, butterscotch-like tastes are particularly desirable for many uses in foodstuff flavors, medicinal product flavors and/or chewing gum flavors. Green, sweet, sharp, strawberry, fruity, strawberry-like, sweet, cheesy, animal, berry, green, pear and banana notes are desirable in perfume compositions. Notes having Turkish-like characteristics as well as aromatic, sweet, bitter, woody, smokey, sour, fruity and green notes are desirable in tobacco flavoring compositions.
U.S. Pat. No. 3,499,769 issued on Mar. 10, 1970 discloses processes for imparting a fresh fruity flavor (particularly strawberry flavor) to foods by adding a small amount of 2-methyl-2-pentenoic acid to the foodstuff.
Arctander, "Perfume and Flavor Chemicals", 1969 discloses the use in perfume compositions and flavors of 4-pentenoic acid, thus:
". . . only rarely used in perfume compositions mainly on fruity bases and certain artificial essential oils. PA1 It finds use in flavors on account of its sour-caramellic taste, pleasant at levels below 10 ppm, and including an almost sweet aftertaste. Higher concentrations have acrid taste and repulsively acid odor, pungent and irritating. PA1 Traces, equivalent to 1 to 5 ppm, are used in imitation butter flavor and in various fruit flavor complexes, e.g., apple, pineapple, apricot and strawberry." PA1 "Spicy-rooty, sweet-sour herbaceous odor of moderate tenacity." PA1 1. Chem. Abstracts 47:4318i -- Colonge, J. Domensh, R.-Bull.Soc.Chim.Franc 634-7(1952) -- By esterification of acid (Trans ethyl ether). PA1 2. Chem. Abstracts 59:2795a -- McGreer, D. E. et al., Can.J.Chem. 41, 726-31 (1963) Trans methyl ester by pyrolysis of 3,5-dimethyl-3-carbomethoxy .DELTA..sup.1 -pyrazoline. PA1 3. Chem. Abstracts 61:14522c -- Tsuji, J. et al., J.Am.Chem.Soc. 86 (20) 4350-3 (1964) --allylic compounds with PdCl.sub.2. PA1 4. Chem. Abstracts 63:P501c -- Fr. Pat. No. 1,389,856, Feb. 19, 1965 (To Toyo Rayon Co.) Synthesis of Trans beta, alpha- unsaturated carboxylic esters. PA1 5. Chem. Abstracts 63:6851c -- Brewis, S. and Hughes, P. R. -- Chem. Commun. (8) 157-8 (1965). Trans esters from conjugated dienes in the presence of carbon monoxide at 1000 atm. PA1 6. Chem. Abstracts 21388f -- Bordenca, C. and Marsico, W. E. Tetrahedron Lett. (16), 1541-3 (1967). Trans esters by carbonylation of piperylene in the presence of PdCl.sub.2. PA1 7. Chem. Abstracts 75:75686k -- Felkin, H. et al -- Ann.Chim. (Paris) 6(1), 17-26 (1971) Cis Ester by reaction of allylmagnesium bromide with acetone. PA1 8. Chem. Abstracts 75:109792j -- Hosaka, S. and Tsuji, J. -- Tetrahedron 27(16) 3821-9 (1971) Trans ester by carbonylation of piperylene in the presence of PdCl.sub.2. PA1 2. Eglinton et al., J.Chem.Soc. (1954) 3197 discloses the reduction of ethyl-2,3-butadienoate to ethyl-3-ethoxy-2-butenoate using sodium ethylate; as well as the partial catalytic hydrogenation of 2,3-butadienoic acid in the presence of 1.5% palladium on calcium carbonate to produce "essentially pure" cis-crotonic acid, according to the following reaction: ##STR8## PA1 7% trans-methyl-2-methyl-2-butenoate; PA1 87% cis-methyl-2-methyl-2-butenoate; PA1 2% "saturated material"; and PA1 4% methyl-2-methyl-3-butenoate PA1 b. Palladium on carbon; or PA1 c. Palladium on calcium carbonate (Lindlar catalyst) at a temperature in the range of from about 10.degree. C up to about 100.degree. C; a hydrogen pressure in the range of from about 5 psig up to about 80 psig, the concentration of said catalyst based on weight of the starting material, the alkyl-2-methyl-3,4-pentadienoate, being from about 0.1% up to about 10%; PA1 Parahydroxy benzyl acetone; PA1 Vanillin; PA1 Maltol; PA1 Ethyl-3-methyl-3-phenyl glycidate; PA1 Benzyl acetate; PA1 Ethyl butyrate; PA1 Methyl cinnamate; PA1 Methyl anthranilate; PA1 Alpha-ionone; PA1 Gamma-undecalactone; PA1 Diacetyl; PA1 Anethole; PA1 Cis-3-hexenol; PA1 2-(4-hydroxy-4-methyl pentyl) norbornadiene (prepared according to Example II of application for U.S. Letters Pat. Ser. No. 461,703 filed on Apr. 17, 1974); PA1 Beta-ionone; PA1 Isobutyl acetate; PA1 Dimethyl sulfide; PA1 Acetic acid; PA1 Acetaldehyde; PA1 4-(2,6,6-trimethyl-1,3-cyclohexadiene-1-yl)-2-butanone (prepared according to Example XVI of application for U.S. Letters Pat. Ser. No. 386,320 filed on Aug. 7, 1973); PA1 4-(6,6-dimethyl-2-methylene-3-cyclohexen-1-yl)-2-butanone (prepared according to Example XVI of application for U.S. Pat. No. 386,320 filed on Aug. 7, 1973); PA1 Geraniol; PA1 Ethyl pelargonate; PA1 Isoamyl acetate; PA1 Naphthyl ethyl ether; PA1 Ethyl acetate; PA1 Isoamyl butyrate; PA1 2-Methyl-2-pentenoic acid; PA1 2-Methyl-3-pentenoic acid; PA1 Elemecine (4-allyl-1,2,6-trimethoxy benzene); PA1 Isoelemecine (4-(1-propenyl)-1,2,6-trimethoxy benzene)
at Volume II, No. 2452. Arctander also discloses the use of trans-2-methyl-2-butenoic acid (tiglic acid) at Vol. II, No. 2949 in perfumery:
and the use of 2-methyl-cis-2-butenoic acid (angelic acid) and alkyl esters thereof in perfumes and flavors at Vol. I, No. 238.
Rossi and Ingrosse, Chem.Abstra. 69, 95851 (g) (Abstract of Gazz.Chim.Ital. 98(7), 866-83 (1968) ) discloses the preparation of 2-methyl-4-pentenoic acid by reacting 3-chloropropene-1 with 1,1-dicarboethoxyethane.
De Moura Campos and de Amarat, Chem.Abstr. 63: 4159(e) (Abstract of J.Arch.Pharm. 298(2), 92-100 (1965) discloses the preparation of 2-methyl-4-pentenoic acid by the following reaction sequence: ##STR4##
Trace and Gurante, Chem.Abstr. 55:14324(i) Abstract of Rend.Inst.Lombardo Sci. Pt.I,Classe Sci. Mat. e Nat., 94A, 309-330 (1960) discloses a process for preparing 2-methyl-4-pentenoic acid by reacting 2-cyclopropyl -propionic acid with HBr.
Adler and Brachel Chem.Abstr. 57: 2042(d) (Abstract of Ann. 651, 141-53 (1962) sets forth a process for giving 12% yields of methyl-2-methyl-4-pentenoate by means of the following reaction: ##STR5##
In the prior art, a number of methods are known for producing the lower alkyl esters of 2-methyl-3-pentenoic acid but either they do not produce isomeric mixtures having desirable aroma and taste impressions or they are not considered to be economical:
Although the prior art contains no suggestion for producing such materials by means of hydrogenation of esters of 2-methyl-3,4-pentadienoic acid, the following references do teach reduction of allenic dienes by means of hydrogenation:
1. U.S. Application for Letters Patent Ser. No. 490,717 filed on July 22, 1974 discloses a process for preparing isomer mixtures containing major proportions of 2-methyl-cis-3-pentenoic acid by first reacting methyl acetylene with a methyl magnesium halide to form a methyl acetylene magnesium halide Grignard reagent; then reacting the methyl acetylene magnesium halide Grignard reagent with acetaldehyde to form a 3-pentyn-2-ol magnesium halide salt; then hydrolyzing the magnesium halide salt to form 3-pentyn-2-ol; then halogenating the 3-pentyn-2-ol to form a 4-halo-2-pentyne; then reacting magnesium with the 4-halo-2-pentyne to produce a 4-magnesium halo-2-pentyne Grignard reagent; then reacting the 4-magnesium halo-2-pentyne Grignard reagent with carbon dioxide to form a magnesium halo-carboxylate salt mixture of compound having the structures: ##STR6## (wherein X is halogen); the hydrolyzing the magnesium halo-carboxylate salt mixture to form a mixture of carboxylic acids having the structures: ##STR7## then hydrogenating the aforementioned mixture of carboxylic acids to form a mixture containing 80% cis-2-methyl-3-pentenoic acid and 20% of 2-methyl-2-pentenoic acid.
3. Bhagwat and Devaprabhakara, Tetrahedron Letters No. 15, pp 1391 - 1392, 1972 ("Selective Hydrogenation of Allenes with Chlorotris (triphenylphosphine) Rhodium Catalyst") discloses the hydrogenation of 1,2,6-cyclononatriene to form cis, cis-1,5-cyclononadiene.
4. Moore, J.Am.Chem.Soc. (84) 3788 discloses the hydrogenation of 1,2-cyclodecadiene using a 10% Pd on charcoal catalyst to produce 17-32% trans-cyclodecene.
5. Meyer and Burwell, J.Am.Chem.Soc. (85) 2881, Oct. 5, 1963 discloses the hydrogenation of 1,2-butadiene using a Pd on alumina catalyst to produce a mixture containing 53% cis-2-butene, 7% trans-2-butene and 40% 1-butene.
6. Rieche et al., Brennstoff Chem. 42, 177 (1961) discloses the liquid phase hydrogenation of 1,2-butadiene using a Pd-BaSO.sub.4 catalyst to yield 44.5% 1-butene; 3.3% trans-2-butene and 52.2% cis-2-butene.
7. Hennien and Sheehan, J.Am.Chem.Soc. 71, 1964 (June, 1949) discloses hydrogenation over a Raney nickel catalyst of 1,2-hexadiene to "produce a mixture of 1- and 2-hexenes in which the latter appear to dominate".
8. Hennion and DiGiovanna, J.Org.Chem. 30, 3696 (Nov. 1965) discloses the hydrogenation over a Raney-nickel catalyst of quaternary ammonium salts according to the following reaction: ##STR9## to yield "a mixture of two possible geometric isomers".
9. Crombie et al., Tetrahedron Letters No. 44, pp. 4297-4302, 1967 ("The Stereochemistry of the Palladium-Catalysed Hydrogenation of Allenes") discloses in Ex. 12 hydrogenation of methyl-2-methyl-3,4-butadienoate over a 5% Pd on BaSO.sub.4 catalyst to yield:
according to the following reaction: ##STR10##
The foregoing prior art does not give rise to any logical prediction of the outcome of carrying out the process of the instant invention.